The study by researchers at the University of Helsinki utilised eye gaze tracking to demonstrate how dogs view the emotional expressions of dog and human faces. Dogs looked first at the eye region and generally examined eyes longer than nose or mouth areas.

Species-specific characteristics of certain expressions attracted researchers' attention, for example the mouths of threatening dogs. However, dogs appeared to base their perception of facial expressions on the whole face.

Threatening faces evoked attentional bias, which may be based on an evolutionary adaptive mechanism, the researchers said."The tolerant behaviour strategy of dogs toward humans may partially explain the results.

Domestication may have equipped dogs with a sensitivity to detect the threat signals of humans and respond them with pronounced appeasement signals," said researcher Sanni Somppi. The study was published in the January 13 issue of science journal PLOS ONE.